DE 42 17 303 A1 discloses a fan unit which is supplied from an auxiliary operation power supply system. The fan unit is used for cooling a diesel engine in a diesel electric locomotive. An auxiliary generator is used to supply electrical power to the auxiliary operation power supply system. The fan unit is driven by a motor.
In the case of diesel electric locomotives, in particular in the case of those of North American type, one or more three-phase auxiliary generators are provided in order to supply the auxiliary appliances, and are connected to the diesel engine. In this case, voltage and frequency fluctuations occur in the electrical power supply system for the auxiliary appliances, which is fed from the auxiliary generator, owing to the variable rotation speed of the diesel engine. Until now, it has therefore been normal to connect contactors, converters or phase gating controllers upstream of the auxiliary appliances.
In order to make it possible to supply the auxiliary appliances with electrical power all the time, it has until now been necessary for the diesel engine always to be operated at an appropriately high rotation speed. Even when the locomotive is being braked and, in consequence, the drive apparatus does not require any power to be supplied to it, it is necessary to continue to operate the diesel engine at an appropriate rotation speed solely for the auxiliary appliances. The rotation speed of the diesel engine is thus at times governed solely by the auxiliary appliances. A further disadvantage is that the auxiliary appliances cannot be supplied if the auxiliary generator fails. In this situation, the entire locomotive is unserviceable, since the auxiliary appliances are required for correct operation.